It is generally known that it is possible to reduce aerodynamic friction resistance and overall drag on the skin of an aircraft, by sucking away at least a portion of the air forming the boundary layer along the aerodynamic surfaces of the outer skin of the aircraft, especially at flow critical areas. Various embodiments and configurations of systems for achieving such boundary layer control by suction are known in the art. For example, German Patent Laying-Out Publication DE-AS 1 280 057 discloses a system for sucking boundary layer air away from an aircraft wing, wherein a suction source located in the interior of the aircraft is connected to the suction passages in the wings by a duct system including suction lines such as pipes or hoses. Details regarding the structure and functioning of the suction source arranged in the interior of the aircraft are not disclosed.
German Patent Laying-Open Publication 197 20 069 and German Patent Laying-Open Publication 196 34 296 each disclose a system for reducing noise emissions and achieving a boundary layer control in connection with a bypass jet engine. One or more hollow air chambers are provided in the nacelle or housing wall of the engine. The outside of the housing wall is provided with corrugations or fluted channels for directing the boundary layer air flow along the housing, and respective openings passing through the housing wall into the hollow chamber from the fluted channels. Further openings pass through the inner wall to connect the hollow chamber or chambers with the bypass channel of the engine.
With such a known structure, at least a portion of the boundary layer air flowing along the outer surface of the engine housing is sucked through the hollow chambers and into the engine bypass channel, as a result of a suction effect created by the supersonic bypass flow being blown through the bypass channel by the fan of the engine. The suction air being sucked through the hollow chambers and into the bypass channel forms a subsonic flow that surrounds the higher velocity active bypass flow and is emitted out of the tail end of the engine together therewith. Thereby, the subsonic flow surrounding or enclosing the supersonic bypass flow is intended to reduce the noise emissions. By also providing a suction flow into the bypass channel upstream of the fan, the flow velocity along the tips of the fan blades is reduced, whereby the forward noise emissions from the fan are intended to be reduced. Both references generally mention that the arrangement of forward-aft extending fluted channels on the outer surface of the engine housing with suction holes therein could also be provided on other surfaces of the aircraft, such as the fuselage and the wings, and that these other surfaces could be pneumatically connected to the suction effect provided by the engine fan in order to achieve a boundary layer control on these surfaces.
German Patent Laying-Open Publication 196 17 952 and corresponding U.S. Pat. No. 5,884,873 (Breit) issued Mar. 23, 1999, disclose a suction generator system including at least one ejector or jet pump for generating a suction flow that is used to suck at least a portion of the boundary layer air through suction holes provided in the aircraft skin. The ejector or jet pump is operated by any selected one or more of several airflow sources, including the pressure differential between the pressurized passenger cabin and the ambient exterior environment, and a flow of high pressure tap or bleed air from at least one engine.
The prior art has not been able to provide an economical and easily adaptable system using one or more suction sources to achieve suction and control of the boundary layer air flow over relatively large surface areas of an aircraft, using the high mass flow of air being moved by an air breathing engine, such as the bypass flow of a high bypass ratio fanjet or turbofan engine, as the primary driving force for the suction generation. Particularly, the prior art solutions have not been shown to achieve an adequate suction flow to provide the required boundary layer control over large surface areas of the aircraft using only the bypass flow of an engine as the driving force for the suction generation. The prior art systems also generally require specialized construction of the aircraft engine or engines, and are not easily retro-fittable in existing aircraft.